Although drug therapies have greatly improved blood pressure (BP) control and reduction of cardiovascular events, as many as 50% of hypertensives on drug treatment have inadequately controlled BP, due to poor adherence, insufficiently aggressive treatment, and an aversion on the part of many patients to drug treatment. Device-guided breathing is a behavioral intervention that guides the breathing rate into the 6 per minute range, inducing respiratory sinus arrythmia (RSA), which is the natural cycle of arrythmia that occurs through the influence of breathing on the flow of sympathetic and vagus impulses to the sinoatrial node of the heart. It has been shown in several small trials to have substantial effects on BP reduction, has no known side-effects, and may represent a cost-effective adjunctive treatment for hypertension. An important consideration is that, often, behavioral interventions are given for a brief amount of time, but are expected to have long-term effects. This does not hold true for medication;one would not give anti-hypertensive medication for eight weeks and expect an effect on BP a year later. The development of behavioral interventions needs to take into account methods to sustain long-term effects. Our aim is to conduct a randomized controlled trial (RCT) to test the efficacy of a guided breathing intervention on ambulatory BP(ABP) in hypertensives drawn from primary care and specialty hypertension practices, using a sample size powered to detect effects at 8 weeks and 4-month follow-up. We also propose to study a physiological mechanism, baroreflex sensitivity, that may mediate the effect of the intervention on BP. The design calls for two control groups: Usual Care (DC) and a placebo condition (using a device that gives the same type of feedback sounds as the guided-breathing feedback device, but which does not guide the breathing rate);and two intervention conditions. In both, the intervention lasts eight weeks, following which participants are further randomized to a) ending the intervention;or B) continuing the intervention for the study duration of 4 months. The main outcome is change in systolic ABP between conditions.